The present invention relates to a clamping chuck for a machine tool.
For a long time such chucks have been known, in which each jaw comprises a support piece slidably mounted in a radial groove in the chuck body, a clamping part slidably mounted in a radial groove in the body or the support piece, a bolt movable axially inside the support piece and provided with teeth capable of cooperating with a toothing of the clamping part so as to fix the latter relative to the support piece, an actuating member movable relative to the support piece and capable of passing from a first position, where it keeps the bolt engaged with the toothing of the clamping part, to a second position, where it keeps the bolt disengaged relative to the clamping part, the chuck comprising moreover an operating ring, which is able to perform an axial sliding action, and means for transforming this axial sliding action into radial displacement of the support pieces of the jaws relative to the chuck body. Such chucks are described, for example, in US-A-3,682,491. They enable the clamping parts to be rapidly changed or rapidly adapted to different sized workpieces.
Such chucks pose a danger because of their structure: when a clamping part is changed or removed, an incorrect maneuver may actuate the operating ring, thereby possibly damaging the tool or even injuring the operator. Electrical safety devices or the like are of course provided, but it is still possible that an accident may occur as a result of carelessness or incorrect operation of the safety devices.
DE-A-3,434,308 proposed an actuating member comprising a locking part which cooperates with a part of the operating ring having a matching shape, the actuating member being provided with a projection which penetrates into a cavity in the operating ring, these two parts cooperating when the drive member is in the second position, i.e. during disengagement of the clamping part, and the operating ring is in the corresponding position, such that displacement of the actuating member is possible only in a defined position of the operating ring.
According to this document, the bolt is operated by means of a rectilinear cam surface which is oblique relative to the radial direction and mounted on the operating member. Consequently, there is imprecision with regard to the relative position when the bolt is disengaged and the operating ring is locked, which may result in an accident.
The object of the present invention is to overcome this drawback.